1. Field of the Invention
The present application relates to the field of antimicrobial agents. The present application also relates to methods of inhibiting microbial growth using human derived peptides.
2. General Background and State of the Art
The mucosal tracts including oral and nasal cavity are exposed to a large spectrum of pathogenic and commensal microorganisms1. The mucosal integrity is preserved by various defense processes including physical barrier, luminal secretions such as mucins, antibacterial substances, the mucosal immune system, and the ability of the mucosa for rapid healing1-6. The homeostasis and integrity of the gastrointestinal mucosa ultimately depend upon a balance between defensive and aggressive factors. The mucosal barrier function was known to play a major role in mucosal protection against luminal bacteria, but the discovery of Toll-like receptors and antimicrobial peptides in the intestinal epithelium has opened a new concept of intestinal defense7-9. The oral cavity is known to teem with complex ever changing spectrum of large microbial populations and sustains repeated abrasions, yet maintains healthy mucosal integrity. Salivary secretions not only have essential functions in the digestive process but also play a critical role in protecting epithelium and mucosa from infection by batteries of secreted proteins, i.e. salivary mucins, proline-rich proteins, IgA, cystatins, elafin, protease, lysozyme, lactoferrin, lactoperoxidase, histatins, and also contains antimicrobial peptides such as defensins, and cathelicidin8,10-12. Antimicrobial peptides are the gene-encoded effector molecules of the innate immune system from insects to humans13,14. The peptides are active against a broad spectrum of Gram-positive and Gram-negative bacteria as well as some fungi and enveloped viruses3,15,16. These peptides play a major role in the management of the normal microflora. In mammals, the antimicrobial peptides are great contributors to antimicrobial efficacy of phagocytes such as neutrophils and macrophages, but the peptides are also expressed in epithelial cells17. In humans, there are three known families of antimicrobial peptides called defensins, cathelicidin and dermicidin. Defensins are divided into the α-defensins found in neutrophils, macrophages, and Paneth cells in the small intestine, and the β-defensins, which are found widespread in epithelial cells18,19. Cathelicidin is found mainly in neutrophils16,20,21. Members of this protein family share a highly conserved N terminus of 12 kDa named cathelin. Dermicidin is primarily found in the sweat gland although it was also expressed in skin and nerves22.
During the investigation of orphan genes yet to be defined for their role in the human salivary gland, a clone was isolated from the subtracted cDNA library of human submandibular gland that was found to be non-redundant in the GenBank database (National Center for Biotechnology Information, NCBI), European Molecular Biology Laboratory (EMBL), and DNA DataBank of Japan (DDBJ), which also showed a characteristic positive expression in the salivary epithelium by RNA in situ hybridization. The C77-91 orphan gene was intensely expressed in the interlobular ductal and some serous acinar cells of human submandibular gland and was named “mucocidin” that expresses 46 amino acids peptide (pl=9.45) possessing an antimicrobial activity on E. coli, Staphylococcus aureus, Pseudonomas aeruginosa, Aspergellous niger, and Candida albicans. The gene encoding mucocidin is the same as the salvic gene registered in Genbank (AY177672)23. Mucocidin consists of a typical hydrophobic amino acid rich domain in the N-terminus and multiple consensus sequences of phosphorylation site and a single glutamine residue that may serve as a possible crosslinking site catalyzed by transglutaminase and four basic amino acids in the C-terminus. Northern blot analysis, in situ hybridization, gene micro-array dot blot analysis and immunohistochemical staining of human organs and tissues using the antibody against the synthetic mucocidin peptide showed that it is widely expressed in various tissues and organs and more so in gastrointestinal tract and exocrine glandular ductal epithelium.